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Updating Lampi Code

Assignment Part 1

In this Assignment you will update the code in the three Lampi applications:

  • lamp_service.py - the hardware daemon
  • main.py - the Kivy UI client
  • lamp_cmd - the command-line client tool

client State

To prevent unwanted feedback, modify all three applications to support the client variable in lamp/set_config and lamp/changed messages, as described in Preventing Unwanted Feedback.

Specifically:

  • lamp_service.py
    • should store client in the database whenever the state is updated (pick a default value to store in the database if there's no value at startup; an empty string '' is a good choice)
    • should ignore as invalid any incoming message on lamp/set_config that does not contain client
    • should publish the value of client from the database in lamp/changed messages
  • main.py - the Kivy Client
    • should include a value in client when publishing a message on lamp/set_config of 'lamp_ui'
    • should ignore any incoming messages on lamp/changed where client is equal to 'lamp_ui'
  • lamp_cmd - the command-line tool
    • should include a value in client when publishing a message on lamp/set_config of 'lamp_cmd'
    • (it doesn't suffer from the feedback issue, so ignoring messages not important)

Quality of Service

We have been using the Paho library defaults of QoS 0 so far. The messages we are sending currently are important enough that users will observe unexpected behavior if they are not received. We will fix that.

Update all three apps to use QoS 1 on all messages published and topic subscriptions.

Client_ID

Each application should specify a MQTT client_id (passed into the Paho Client consturctor):

  • lamp_service.py should use a client_id of "lamp_service"
  • main.py should use a client_id of "lamp_ui"
  • lamp_cmd should use a client_id of "lamp_cmd"

Connection Status

It will be handy to observe the MQTT connection status of our two long-running services, "lamp_service.py" and "main.py".

Modify both of them to have the following behavior.

When connecting, each service should specify a Will with the following values:

  • a Payload of "0"
  • a topic of lamp/connection/<client_id>/state
  • Retain True
  • a QoS of 2

where <client_id> is the same as the service's <client_id> specified above.

Immediately after connecting to the broker, each service should publish a message:

  • a Payload of "1"
  • a topic of lamp/connection/<client_id>/state
  • Retain True
  • a QoS of 2

Using mosquitto_sub on the Pi, prove that the services state is being published properly, by killing one service at a time and observing the state change.

Next up: go to Supervisor for Lampi

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